Cabin Heating & Cooling Systems

Introduction:

  • Cabin Heating and cooling systems provide conditioned air for comfortable operations during various weather conditions
  • Cabin heat is the system used to condition the air for the pilot and passenger's comfort during colder months and higher altitudes
  • Cooling systems, while clearly designed to do the opposite of heating systems, are less prolific, but still exist

Cabin Heating Systems:

  • Exhaust Manifold Heat Exchanger:

    • Heat Exchanger
      Heat Exchanger
    • Inlet air is bypassed through an exhaust shroud
    • Air is ducted from exhaust shroud, now heated, into ventilation ducts inside of the cabin [Figure 1]
    • Heat Exchanger
      Heat Exchanger

  • Combustion Heater:

    • Hartzell Combustion Heater Assembly
      Hartzell Combustion Heater Assembly
    • Uses fuel from the aircraft fuel system to support a flame in a designated heater unit
    • Air enters the combustion chamber by use of a fan or ram air where it is then burned inside a shroud [Figure 2]
    • The resulting warm air from the shroud is routed into the cabin while the exhaust gas is vented overboard
    • Heat is regulated with a thermostat
    • Hartzell Combustion Heater Assembly
      Hartzell Combustion Heater Assembly

  • Coolant Heat Exchanger:

    • Coolant from the engine's cooling system is fed into the cabin and to a heat exchanger
    • This heat exchanger blows air across a radiator, heating the air, and therefore the cabin
    • This system is uncommon because it requires engines be liquid cooled when most are in fact air cooled
    • This system is the same as that in your car

  • Cabin Heat Malfunctions:

    • Exhaust pipes may burst allowing carbon monoxide to enter the cabin
    • Heaters may have the same problem with the internal combustor

Common Training Aircraft Heating and Cooling Characteristics:

  • Cessna 172:

    • Temperature and intensity adjusted with push-pull labeled CABIN HT and CABIN AIR
    • Air enters from wing and nose inlet vents
    • Air heated with a heat exchanger with a shroud over exhaust pipes

  • Piper Arrow:

    • Temperature and intensity adjusted with sliders
    • Air enters from wing and nose inlet vents
    • Air is heated with a heat exchanger with a shroud over exhaust pipes
    • Additional air enters from the aft fuselage

Conclusion:

  • Carbon Monoxide Poisoning in a silent killer who's risk can be mitigated through a few simple steps
  • Especially in winter months, refresh your knowledge on Carbon Monoxide and conduct an extra thorough preflight
    • Remember, the heater system may have gone unused for months
  • You can find more information about your aircraft in Chapter 7 of the Pilot Operating Handbook
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References: